The present invention relates to a two-layer clad pipe and a method for making the same. More specifically, the present invention relates to a two-layer clad pipe with an outer pipe outwardly fitted to an inner pipe and a method for making the same. A xe2x80x9ctwo-layer clad pipexe2x80x9d is different from a two-layer pipe where there is a gap between the inner pipe and the outer pipe. What is referred to is a pipe in which the outside of the inner pipe is covered by the outer pipe and the two pipes are pressed integrally against each other.
Conventional metal pipes are generally single-layer structures since they are usually made with drawing operations. While pipes in which a synthetic resin film layer is formed on the inner surface of a metallic outer pipe are used in practice, metallic two-layer pipes are currently not available.
Conventional metal piper are also formed by creating of holes at the center of metal rods, by drilling using machine tools such as drill presses. While drills, capable of drilling small-diameter holes of 100-300 microns, are available, these drills are limited to forming holes with a depth of about three times the drill diameter. Thus, drilling is not able to provide a cylindrical through-hole. Also, while drawing can be performed to shape pipes in various irregular, non-circular shapes, it is almost impossible to form small-diameter pipes with small holes of no more than approximately 1 mm diameter.
An optical communication system structure has optical connectors connected to the ends of multiple optical fibers and optical connectors connected to each other through optical adapters. In these conventional optical communication systems, a connection ferrule is mounted at the end of each optical fiber, and an alignment sleeve is disposed in the optical adapter. A connection is made by inserting a pair of connection ferrules into the ends of an alignment sleeve, and the end surfaces of the cladding of the optical fibers are abutted against each other.
Referring to FIGS. 18(a) and 18(b), a connection ferrule 50 is formed from a main ferrule unit 51 and a zirconia cylinder 52. A core guiding hole 53 (e.g., 800 microns inner diameter, 2.5 mm length) is formed in main ferrule unit 51 to guide the core of an optical fiber. A cladding guiding hole 56 (e.g., 125 microns inner diameter, 5 mm length) is formed in cylinder 52 to guide the cladding of the optical fiber. A fitting section 54 is formed on main ferrule unit 51 to fit the fitting hole of the optical connector.
With pipes having a single-layer structure, everything from the inside to the surface of the pipe is formed from the same metal. Thus, these pipes are not suitable for cases where different functions are demanded for the inner surface and the outer surface of the pipe. For example, there are cases where the inner surface and the outer surface of a pipe should have different corrosion resistance, strength, conductivity, magnetism, wear characteristics, heat characteristics, ease of cutting, specific density, or the like. However, pipes with single-layer structures are not able to meet these needs. For example, for pipes carrying corrosive fluids, the entire pipe would be made from a corrosion-resistant metal. Thus, the specifications for the outer surface of the pipe would be needlessly high, resulting in increased production costs for the devices and equipment.
Also, with pipes made using conventional drawing operations involving dies and plugs, the inner diameter cannot be less than 1 mm. No suitable technology has been established for producing small- diameter pipes. As a result, production of ring-shaped or cylindrical precision metal pipes from pipes is difficult. Also, while holes with irregular cross-sections can be formed in pipes through drawing, these holes formed by drawing can be slightly larger or smaller than the plug diameter, making it difficult to improve the precision of the hole.
Referring to FIGS. 18(a) and 18(b), a thin hole with an inner diameter of approximately 125 microns cannot be formed in a metal member, so the connection ferrule must be formed from a main ferrule unit and a separate cylinder, making the connection ferrule very expensive.
It is an object of the present invention to provide a two-layer clad pipe which overcome the foregoing problems.
More specifically, it is an object of the present invention to provide a two-layer clad pipe in which the inner surface and the outer surface are formed from metals suited for their required functions.
Another object of the present invention is to provide a two-layer clad pipe that can be used in various applications.
Yet another object of the present invention is to provide a method for making a two- layer clad pipes.
A two-layer clad pipe according to the present invention includes a metal inner pipe and an outer pipe outwardly fitted tightly against an outer perimeter surface of the inner pipe. The outer pipe is formed from a metal different from a metal used to form the inner pipe.
Since the inner pipe and the outer pipe in this two-layer clad pipe are formed from different metals, the inner pipe and the outer pipe can be formed with metals suited for their respectively required functions.
There are no restrictions on the diameter of the inner pipe, and various sizes can be provided. Similarly, there are no restrictions on the diameter of the outer pipe, and various sizes can be provided. The inner pipe can have thin walls or thick walls. Similarly, the outer pipe can have thin walls or thick walls. There are no particular restrictions on the diameter of the hole in the inner pipe, and various diameters can be used. The cross-section shape of the outer pipe is not restricted to a circular shape and non-circular irregular shapes can be used. The metals used in the inner pipe and the outer pipe can be selected from steel, stainless steel, copper and alloys thereof, aluminum and alloys thereof, titanium and alloys thereof, magnesium and alloys thereof, and the like. However, the inner pipe and the outer pipe must be formed from metals that can be shaped by drawing.
For example, a two-layer clad pipe with a stainless steel inner pipe and a standard steel outer pipe will have a corrosion-resistant inner surface and can be used for various applications. A two-layer clad pipe having an aluminum inner pipe and a stainless steel outer pipe with relatively thin walls will have a corrosion-resistant outer surface and will be light, allowing it to be used for various applications.
A method for making a two-layer clad pipe according to the present invention includes a first step for producing a metal outer pipe by drawing and producing an inner pipe by drawing. The inner pipe is formed from a metal different from that used in the outer pipe. A second step involves inserting the inner pipe into the outer pipe and inserting a metal core into the inner pipe. A third step involves drawing the outer pipe and the inner pipe with the inserted metal core so that the inner pipe is pressed tightly against the metal core and the outer pipe is pressed tightly against an outer perimeter surface of the inner pipe. A fourth step involves pulling out the metal core from the inner pipe.
By drawing the pipes with the metal core inserted, shaping is performed without the plug of the drawing device, using a die only. This provides an increased degree of freedom in shaping, and allows two-layer clad pipes having different cross-section shapes to be produced. The metal core can be used repeatedly. The diameter, thickness, metals, and cross-section shapes of the inner pipe and the outer pipe are the same as with the two-layer clad pipe.
Since the two-layer clad pipe is made by drawing, the inner pipe and the outer pipe with the inner pipe inserted into the outer pipe, and the metal core inserted in the inner pipe, the outer pipe can be tightly pressed against the inner pipe and the outer pipe can be tightly pressed against the metal core. Thus, the inner pipe and the outer pipe are pressed suitably tightly against each other, providing a high-quality pipe.
Since the metal core is pulled out after the drawing operation, the metal core allows the two-layer clad pipe to be formed with a hole having the same cross-section shape as the metal core. The cross-section shape of the metal core does not have to be circular and can be various non-circular irregular shapes. The thickness (diameter) of the metal core can be selected freely within the restriction imposed by the diameter of the inner pipe. For example, a thin metal core having a diameter of about 100 microns can be used.
Another method for making a two-layer clad pipe according to the present invention includes a first step for producing a metal outer pipe by drawing and producing an inner pipe by drawing. The inner pipe is formed from a metal different from that used in the outer pipe. A second step involves inserting the inner pipe into the outer pipe. A third step involves drawing the outer pipe and the inner pipe with the inner pipe inserted into the outer pipe so that the outer pipe is pressed tightly against an outer perimeter surface of the inner pipe. The diameter, thickness, metals, and cross-section shapes of the inner pipe and the outer pipe are the same as with the two-layer clad pipe.
In this invention, the inner pipe and the outer pipe are drawn without the use of a metal core. In the first step, the inner pipe and the outer pipe are formed by drawing. The inner pipe and the outer pipe are formed using different metals. In the second step, the inner pipe is inserted into the outer pipe. Next, in the third step, outer pipe and the inner pipe are drawn with the inner pipe inserted in the outer pipe. This causes the outer pipe to be pressed tightly against the outer perimeter surface of the inner pipe, thus providing a two-layer clad pipe.
Since this invention does not use a metal core, costs involved in inserting, storing, and transporting the metal core are eliminated. Drawing without the metal core is suitable for when the diameter of the hole in the two-layer clad pipe is approximately 1 mm or more.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.